A wide variety of heart valve prostheses have been developed to operate in conjunction with the pumping action of the heart to take the place of defective natural valves. These valves variously have valve bodies which are designed to function with one or more occluders or leaflets to open and close a central blood flow passageway through the valve body.
As a means for inserting heart valves into the heart, the valves commonly have attached fabric members suturable to the tissues of the heart. Frequently the fabric member is attached to a separate suture ring which is applied to the periphery of the heart valve body or orifice ring, for example, as described in U. S. Pat. Nos. 3,763,548 and 4,535,483. Conventional sewing rings or suture rings are made of Dacron (.TM.) fabric which enables a surgeon to suture the prosthetic valve to the residual valve ring after the defective valve has been removed. However, there is some incidence of failure of mechanical heart valves that is attributed to tissue overgrowth from the fabric members into an interference location with the moving mechanical parts of the heart valves.
Another important design consideration for heart valves and their suture rings is minimizing the radial thickness in order to maximize the size of the central blood flow passageway of the heart valve that is inserted in a patient's natural passageway. Thinner heart valve bodies formed, for example, as unitary structures of pyrolytic carbon have enabled larger valve passageways to be provided; however, thin heart valve bodies sometimes lack the rigidity that is desirable for such valves. To improve the stability and rigidity of the heart valve body, the outer surface of many heart valve bodies are often formed with a shallow groove or channel which receives a metal stiffening ring for the valve body, which is otherwise preferably made of a material having some resiliency, such as pyrocarbon or pyrocarbon-coated graphite.
Some existing heart valve and suture ring combinations must be assembled and pre-oriented prior to surgical insertion within the patient. Such pre-orientation contributes to the difficulty associated with the surgeon's task of obtaining the proper fit and proper orientation of the heart valve and suture ring during the insertion operation. A preferable design should allow for easy insertion into the patient after which it may be easily adjusted or oriented to the proper position for suturing to heart tissues.
The opening and closing of heart valves should be sufficiently soft so that the patient is not disturbed by the sounds produced and that the forces imparted on the heart walls are minimal. Nevertheless, the opening and closing of most existing heart valves does impart small axial forces on the valve body which often translate into small axial displacements or deformations of the valve body. The traditional Dacron (.TM.) fabric rings also provide a cushion for the harsh impact on the mechanical parts as the valve closes. To that end, the heart valve body in combination with the suture ring should therefore provide sufficient dampening or resistance to these small axial displacements.
Accordingly, there is a continuing need for improved suture rings which together with the heart valve bodies occupy a narrow region along the heart passageway and can be easily inserted and adjusted within the patient. Further, the heart valve bodies and suture rings which together provide the rigidity needed to assure that the valve body will not be radially deformed during insertion and that axial displacements during valve operation are sufficiently dampened or absorbed. More importantly, the suturing member portion of the improved suture ring should be adapted to prevent or inhibit tissue growth thereon.